Printed wiring board and method for manufacturing the same

ABSTRACT

A printed circuit board is by formed by laminating an interlaminar insulating layer on a conductor circuit of a substrate, in which the conductor circuit is comprised of an electroless plated film and an electrolytic plated film and a roughened layer is formed on at least a part of the surface of the conductor circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/203,427,filed Aug. 15, 2005, which is a continuation of application Ser. No.10/351,501, filed Jan. 27, 2003, now U.S. Pat. No. 6,930,255, issuedAug. 16, 2005, which is a divisional of application Ser. No. 09/319,258,filed Jun. 11, 1999, now U.S. Pat. No. 6,835,895, issued Dec. 28, 2004,which is a National Stage Application of International Application No.PCT/JP97/04684, filed Dec. 18, 1997. This application is based on andclaims the benefit of priority to Japanese Application Nos. 8-354971,filed Dec. 19, 1996, 8-357959, filed Dec. 27, 1996, 8-357801, filed Dec.28, 1996, 9-29587, filed Jan. 28, 1997, 9-197526, filed Jul. 23, 1997,and 9-197527, filed Jul. 23, 1997. The entire contents of thoseapplications are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to a printed circuit board and a method ofproducing the same, and more particularly to a printed circuit boardwhich can control the occurrence of cracks in the heat cycle and preventthe dissolution of the conductor circuit caused by roughening of aninterlaminar insulating layer without the degradation of peel strength,and a method of producing the same.

BACKGROUND ART

Recently, so-called build-up multilayer wiring board are in demand orhigh densification of multilayer wiring boards. This build-up multilayerwiring board is produced, for example, by a method as described inJP-B-4-55555. That is, an insulating agent composed of a photosensitiveadhesive for electroless plating is applied onto a core substrate,dried, exposed to a light and developed to form an interlaminarinsulating resin layer having openings for viaholes, and then thesurface of the interlaminar insulating resin layer is roughened bytreating with an oxidizing agent or the like, and a plating resist isformed on the roughened surface, and thereafter a non-forming portion ofthe plating resist is subjected to an electroless plating to formviaholes and conductor circuits, and then such steps are repeated pluraltimes to obtain a build-up multilayer wiring board.

However, in the thus obtained multilayer printed circuit board, theconductor circuit is formed on the non-forming portion of the platingresist and the plating resist remains in the inner layer as it was.

Therefore, if IC chips are mounted on such a wiring board, there is aproblem that warping of the board is caused by a difference of thermalexpansion coefficient between IC chip and the insulating resin layer inthe heat cycle to concentrate stress into a boundary portion between theplating resist and the conductor circuit due to poor adhesion propertytherebetween and hence cracks are generated in the interlaminarinsulating layer contacting with the boundary portion.

As a technique capable of solving this problem, there is a method ofremoving the plating resist retained in the inner layer and forming aroughened layer on the surface of the conductor circuit to provide anadhesion to the interlaminar insulating layer. For example,JP-A-6-283860 discloses a technique of removing the plating resist inthe inner layer and providing a roughened layer ofcopper-nickel-phosphorus on the surface of the conductor circuitcomposed of an electroless plated film to prevent interlaminar peeling

in the invention of JP-A-6-283860, however, there is no understandingabout cracks caused when the heat cycle test is actually carried outafter the mounting of IC chips, and only a conductor circuit composed ofonly an electroless plated film is disclosed. Moreover, when asupplementary test of the heat cycle at −55° C.-+125° C. is carried out(see Comparative Example 1 as mentioned later), cracking is not observedin about 1000 cycles, but when the cycle number exceeds 1000 cycles,cracking is observed.

As another technique capable of solving the above problem, there isconsidered a method of adopting so-called semi-additive process toremove the plating resist. In the semi-additive process, however, theconductor circuit is comprised of an electroless plated film and anelectrolytic plated film, so that there is a problem that when thesurface of the insulating resin layer is subjected to a rougheningtreatment, a surface portion composed of the electrolytic plated film ofthe conductor circuit is dissolved by the local electrode reaction.

On the other hand, in order to mount IC chips on the printed circuitboard, it is necessary to form a solder bump on the circuit board. As amethod of forming the solder bump, there has hitherto been adopted amethod wherein an alignment mark composed of a conductor layer ispreviously formed on a mask for printing such as a metal mask, a plasticmask or the like and a printed circuit board in order to determinepositioning of the mask for printing and the printed circuit board, andthen both alignment marks are adjusted to each other to laminate themask for printing on the printed circuit board at a given position, andthereafter a cream solder is printed thereon. In this case, a solderresist layer opening a portion of the alignment mark or the pad forsolder bump formation is formed on the printed circuit board.

Therefore, if IC chips are mounted on such a printed circuit board,there is a problem that warping of the board is caused by a differenceof thermal expansion coefficient between IC chip and the insulatingresin layer in the heat cycle to concentrate stress in a boundaryportion between the solder resist layer and the conductor layer(inclusive of the alignment mark and the pad for solder bump formation)due to the absence of adhesion therebetween and hence cracks aregenerated in the solder resist layer starting from the boundary portionand the solder resist is peeled off.

It is, therefore, an object of the invention to solve the aforementionedproblems of the conventional technique.

It is a main object of the invention to provide a printed circuit boardcapable of effectively preventing cracks and interlaminar peeling of theinterlaminar insulating layer created in the heat cycle withoutdegrading other properties, particularly peel strength of conductor(adhesion between a conductor circuit and an interlaminar insulatinglayer, adhesion between a viahole and an under layer conductor circuit,or adhesion between a conductor layer and a solder resist layer).

It is another object of the invention to provide a printed circuit boardcapable of preventing the dissolution of the surface of the conductorcircuit through the local electrode reaction.

It is still another object of the invention to provide a method ofadvantageously producing such a printed circuit board.

DISCLOSURE OF THE INVENTION

The inventors have made various studies in order to achieve the aboveobjects and as a result the invention lying in the followingconstructions has been accomplished.

(1) The printed circuit board according to the invention is a printedcircuit board formed by laminating an interlaminar insulating layer on aconductor circuit of a substrate and repeating formation of conductorcircuit and an interlaminar insulating layer, characterized in that theconductor circuit is comprised of an electroless plated film and anelectrolytic plated film, and a roughened layer is formed on at least apart of the surface of the conductor circuit.

(2) The printed circuit board according to the invention is a printedcircuit board formed by laminating an interlaminar insulating layer on aconductor circuit of a substrate and repeating formation of conductorcircuit and an interlaminar insulating layer, characterized in that theconductor circuit is comprised of an electroless plated film and anelectrolytic plated film, and a roughened layer is formed on at least apart of the surface of the conductor circuit, and the surface of theroughened layer is covered with a layer of a metal having an ionizationtendency of more than copper but less than titanium or a noble metal.

In the printed circuit board described in the item (1) or (2), it ispreferable that the roughened layer is formed on at least a part of thesurface inclusive of a side surface of the conductor circuit and thatthe roughened layer is a plated layer of copper-nickel-phosphorus alloy.

(3) A method of producing the multilayer printed circuit board accordingto the invention comprises steps of subjecting a surface of a substrateto an electroless plating, forming a plating resist thereon, subjectingthe substrate to an electrolytic plating, removing the plating resist,etching and removing the electroless plated film beneath the platingresist to form a conductor circuit comprised of the electroless platedfilm and the electrolytic plated film, forming a roughened layer on atleast a part of the surface of the conductor circuit and then forming aninterlaminar insulating layer thereon.

(4) A method of producing the multilayer printed circuit board accordingto the invention comprises subjecting a surface of a substrate to anelectroless plating, forming a plating resist thereon, subjecting thesubstrate to an electrolytic plating, removing the plating resist,etching and removing the electroless plated film beneath the platingresist to form a conductor circuit comprised of the electroless platedfilm and the electrolytic plated film, forming a roughened layer on atleast a part of the surface of the conductor circuit, covering thesurface of the roughened layer with a layer of a metal having anionization tendency of more than copper but less than titanium or anoble metal and forming an interlaminar insulating layer thereon.

In the method described in item (3) or (4), the roughened layer ispreferably formed by plating of copper-nickel-phosphorus alloy.

(5) The printed circuit board according to the invention is a multilayerprinted circuit board comprising a substrate provided with an underlayer conductor circuit, an interlaminar insulating layer formed thereonand an upper layer conductor circuit formed on the interlaminarinsulating layer, and a viahole connecting both the conductor circuitsto each other, in which the viahole is comprised of an electrolessplated film and an electrolytic plated film, and a roughened layerhaving a roughened surface formed by etching treatment, polishingtreatment, or redox treatment, or having a roughened surface formed by aplated film is formed on at least a part of the surface of the lowerlayer conductor circuit connecting to the viahole.

In the printed circuit board described in item (5), the roughened layeris preferably formed by plating of copper-nickel-phosphorus alloy.

(6) A method of producing the multilayer printed circuit board accordingto the invention comprises forming an under layer conductor circuit on asurface of a substrate, forming a roughened layer on at least a part ofa surface of the under layer conductor circuit to be connected to aviahole, forming an interlaminar insulating layer thereon, and formingopenings for viaholes in the interlaminar insulating layer, subjectingthe interlaminar insulating layer to an electroless plating, forming aplating resist thereon and subjecting the substrate to an electrolyticplating, removing the plating resist, etching and removing theelectroless plated film beneath the plating resist to form an upperlayerconductor circuit comprised of the electroless plated film and theelectrolytic plated film and a viahole.

In the method described in item (6), the roughened layer is preferablyformed by plating of copper-nickel-phosphorus alloy.

(7) A printed circuit board provided with a conductor layer used as analignment mark, in which a roughened layer is formed on at least a partof the surface of the conductor layer.

In the printed circuit board described in item (7), the conductor layeris preferably comprised of an electroless plated film and anelectrolytic plated film.

(8) A printed circuit board provided with a conductor layer used as analignment mark, in which the conductor layer is comprised of anelectroless plated film and an electrolytic plated film.

In the printed circuit board described in item (8), it is preferablethat the roughened layer is formed on at least a part of the surface ofthe conductor layer.

In the printed circuit board described in item (7) or (8), it ispreferable that the alignment mark is an opening portion formed byexposing only the surface of the conductor layer from a solder resistformed on the conductor layer, and it is preferable that a metal layerof nickel-gold is formed on the conductor layer exposed from the openingportion.

Further, in the printed circuit board described in item (7) or (8), itis preferable that the alignment mark is used for positioning to aprinted mask, an IC chip mounting and positioning in the mounting of aprinted circuit board packaged a semiconductor element to anotherprinted circuit board.

BRIEF EXPLANATION OF THE DRAWINGS

FIGS. 1-19 are flow charts showing production steps of a printed circuitboard in Example 1;

FIG. 20 is a triangular diagram showing a composition ofcopper-nickel-phosphorus roughened layer;

FIGS. 21-40 are flow charts showing production steps of a printedcircuit board in Example 5;

FIG. 41 is a partial sectional view showing an alignment mark composedof a conductor layer and used for positioning to a printed mask or an ICchip mounting;

FIG. 42 is a partial sectional view showing an alignment mark composedof a conductor layer and used for positioning in the mounting of aprinted circuit board packaged a semiconductor element to anotherprinted circuit board; and

FIG. 43 is a plane view of a printed circuit board.

In these drawings, numeral 1 is a substrate, numeral 2 an interlaminarinsulating resin layer (an adhesive layer for electroless plating),numeral 2 a an insulating layer, numeral 2 b an adhesive layer, numeral3 a plating resist, numeral 4 an inner layer conductor circuit (an innerlayer copper pattern), numeral 5 an outer layer conductor circuit (anouter layer copper pattern), numeral 6 an opening for viahole, numeral 7a viahole (BVH), numeral 8 a copper foil, numeral 9 a through-hole,numeral 10 a filling resin (a resin filler), numeral 11 a roughenedlayer, numeral 12 an electroless copper plated film, numeral 13 anelectrolytic copper plated film, numeral 14 a solder resist layer,numeral 15 a nickel plated layer, numeral 16 a gold plated layer,numeral 17 a solder bump (a solder body), numeral 18 an alignment mark(used for positioning to a printed mask), numeral 19 an alignment mark(used for positioning to an IC chip mounting), numeral 20 an alignmentmark (used for positioning in the mounting of a printed circuit boardpackaged a semiconductor element to another printed circuit board),numeral 21 a pad for solder bump formation, numeral A a product portion.

BEST MODE FOR CARRYING OUT THE INVENTION

{circle around (1)}. The printed circuit board according to theinvention lies in a point that the conductor circuit is comprised of anelectrolytic plated film and an electroless plated film, and theelectroless plated film is located at an inner layer side and theelectrolytic plated film is located at an outer layer side (see enlargedviews of FIG. 18 and FIG. 19).

In such a structure, since the electrolytic plated film is softer andmore malleable than the electroless plated film, the conductor circuitis able to follow size change of the interlaminar insulating resin layeras an upper layer even if warping of the board is generated in the heatcycle. Moreover, in the printed circuit board according to theinvention, since the roughened layer is formed on the surface of theconductor circuit, the conductor circuit is strongly adhered to theinterlaminar insulating resin layer as an upper layer and more readilyfollows size change of the interlaminar insulating resin layer.

Particularly, it is advantageous to form the roughened layer on at leasta side face of the conductor circuit, which can control cracks generatedin the interlaminar insulating resin layer starting from the boundaryportion between the side face of the conductor circuit and theinterlaminar resin contacted therewith.

{circle around (2)}. The printed circuit board according to theinvention lies in a point that the viahole is comprised of anelectrolytic plated film and an electroless plated film, and theelectroless plated film is located at an inner layer side and theelectrolytic plated film is located at an outer layer side (see enlargedviews of FIG. 18 and FIG. 19).

In such a structure, since the electrolytic plated film is softer andmore malleable than the electroless plated film, the viahole is able tofollow size change of the interlaminar insulating resin layer as anupper layer even if a warp of the board is generated in the heat cycle.Moreover, the viahole in the printed circuit board according to theinvention is constructed at the inner layer side with the hardelectroless plated film and also such an electroless plated film isadhered to the under layer conductor circuit through the roughenedlayer, so that the viahole is not peeled off from the under layerconductor circuit in the heat cycle. Because the metal layer encroachedby the roughened layer is the harder electroless plated film, and hencebreakage at the metal layer is rarely caused even when peeling force isapplied.

In short, when the viahole is comprised of only the electrolytic platedfilm, even if it is adhered to the under layer conductor circuit throughthe roughened layer, the electrolytic plated film itself is soft and isapt to peel off due to the heat cycle. While, when the viahole iscomprised of only the electroless plated film, it can not follow sizechange of the interlaminar insulating resin layer and hence cracking iscaused in the interlaminar insulating resin layer on the viahole. In theprinted circuit board according to the invention, the viahole iscomprised of the electrolytic plated film and the electroless platedfilm and connected to the under layer conductor circuit through theroughened layer, so that the occurence of cracks generated in theinterlaminar insulating resin layer on the viahole, and peeling betweenthe viahole and the under layer conductor circuit in the heat cycle canbe prevented at the same time.

Moreover, when the interlaminar insulating resin layer is roughened, itis desirable that a plated film encroached into the roughened layer ishard. Because breakage is rarely caused at the plated film portion whenpeeling force is applied.

In structure {circle around (2)}, the roughened layer may be formed onthe surface of the viahole. Because the roughened layer is stronglyadhered to the interlaminar insulating resin layer as an upper layer andhence the viahole is more able to follow size change of the interlaminarinsulating resin layer. Further, the roughened layer on the under layerconductor circuit may be formed on not only the portion connecting tothe viahole but also the whole surface of the under layer conductorcircuit. The adhesion of the under layer conductor circuit to theinterlaminar insulating resin layer is improved like the above structure{circle around (1)}.

In structure {circle around (2)}, it is desirable that the under layerconductor circuit connecting to the viahole is comprised of theelectrolytic plated film and the electroless plated film, and theelectroless plated film is located at an inner layer side and theelectrolytic plated film is located at an outer layer side. Because theinner layer side of the under layer conductor circuit is adhered to theinterlaminar insulating resin layer, it is desirably a hard electrolessplated film in order to ensure peel strength, while the contrary side isconnected to the viahole and is desirably an electrolytic plated filmhaving an excellent following property to size change.

{circle around (3)}. The printed circuit board according to theinvention lies in a point that the roughened layer is formed on at leasta part of the surface of the conductor layer as an alignment mark usedfor positioning to a printed mask or an IC chip mounting and as analignment mark used for mounting a packaged board obtained by mounting asemiconductor element onto another printed circuit board (see enlargedview of FIG. 41).

When a peripheral edge of the conductor layer is covered with the solderresist layer (that is, in case of exposing only the conductor layer froman opening of the solder resist layer), peeling of the solder resistlayer is not caused and the function of the conductor layer as analignment mark is not lowered.

{circle around (4)}. The printed circuit board according to theinvention lies in a point that the conductor layer as an alignment markis comprised of the electrolytic plated film and the electroless platedfilm, and the electroless plated film is located at an inner layer sideand the electrolytic plated film is located at an outer layer side, andthe alignment mark is used for positioning to a printed mask or an ICchip mounting and for mounting the packaged board obtained by mounting asemiconductor element to another printed circuit board (see enlargedview of FIG. 41).

In such a structure, since the electrolytic plated film is softer andmore malleable than the electroless plated film, the conductor layer isable to follow size change of the solder resist layer as an upper layereven if warping of the board is generated in a heat cycle. Moreover,when the roughened layer is formed on the surface of the conductorlayer, the conductor layer is strongly adhered to the solder resistlayer as an upper layer and is able to follow size change of the solderresist layer. Further, the conductor contacting with the interlaminarinsulating layer is an electroless plated film and high in the hardness,and hence peel strength can be increased.

Particularly, it is advantageous to form the roughened layer on at leasta side face of the conductor layer, which can control cracks generatedin the solder resist layer or the like starting from a boundary betweenthe side face of the conductor layer and the solder resist layercontacting therewith in the heat cycle.

In the structures {circle around (3)} and {circle around (4)}, it isfurther desirable that the metal layer made of nickel-gold is formed onthe conductor layer as an alignment mark exposed from the openingportion. Because gold is high in reflectance and advantageouslyfunctions as an alignment mark. The metal layer made of nickel-gold maybe formed by electroless plating. For example, the nickel layer iscomprised of a nickel plated film having a thickness of 5 μm, and thegold layer is comprised of a flash gold plated film having a thicknessof 0.1 μm or a thick gold plated film having a thickness of 0.5 μm.

In the structures {circle around (3)} and {circle around (4)}, as shownin FIG. 41, the printed circuit board is comprised, for example, of aninsulating substrate 1, a first layer conductor circuit 4 and aninterlaminar insulating layer 2 (an adhesive layer for electrolessplating) formed thereon, a pad (a conductor pattern) 21 for a solderbump formation comprising a part of a second layer conductor circuit, analignment mark 18 for positioning to a printed mask and an alignmentmark 19 for an IC chip mounting formed on the interlaminar insulatingagent 2 through semi-additive process, a solder resist layer 14 formedon a portion other than the alignment mark 18, 19 and the pad 21 for thesolder bump formation. The alignment mark 18 for positioning to theprinted mask is formed on a portion forming no conductor pattern in thevicinity of an outer peripheral portion of the printed circuit board.Concretely, it is formed, for example, on an outside of a productportion A shown in FIG. 41. Therefore, the alignment mark 19 for the ICchip mounting enables an IC chip mounting without influence of the mark18. In this case, the vicinity of the outer peripheral portion means anoutside portion of the product portion as above mentioned. Further, thealignment mark 19 for the IC chip mounting is formed on each productportion in the printed circuit boards in order to mount an IC chip oneach product portion. Further, in case of mounting a semiconductorelement to produce a packaged board, the alignment mark 20 used formounting the packaged board to another printed circuit board is formedon the innermost side as shown FIG. 42. The alignment mark 20 isdesirably a cross-shaped mark as shown FIG. 43. In case of adopting thecross-shaped mark, an opening of a solder resist layer is formed so asto cover the peripheral edge of the cross.

Particularly, the alignment marks 18, 19 are preferably formed in theopening portions exposing only the surface of the conductor layer fromthe solder resist layer formed on the conductor layer (including theviahole). Because the peripheral edge of the conductor layer overlapswith the solder resist layer and hence the peeling of the conductor canbe prevented by holding the conductor with the solder resist layer asshown FIG. 41. Moreover, in the heat cycle, cracks generated startingfrom the boundary portion between the conductor layer and theinterlaminar insulating resin layer due to the difference of thermalexpansion coefficient can be controlled.

Particularly, the alignment mark for positioning to a printed mask hasthe following effect.

The opening of the solder resist layer is formed by placing a photomaskfilm and subjecting to light exposure and developing treatments. If theposition of the photomask is shifted, the position of the opening isalso shifted.

If the conductor layer as an alignment mark is perfectly exposed, sincea center of the conductor is recognized as the central position of thealignment mark in a camera, position shifting of the opening in thesolder resist layer cannot be recognized. As a result, the openingportion of the printed mask is not coincident with the opening portionof the solder resist layer, so that an opening volume of the printedmask is decreased due to the solder resist layer and the height of asolder bump becomes low.

On the other hand, if the peripheral edge of the conductor layer as analignment mark is covered with the solder resist layer, since a centerof the conductor exposed from the opening portion is recognized as thecentral position of the alignment mark in a camera, even if thephotomask for opening the solder resist layer is shifted to causeposition shifting of the opening in the solder resist layer, thealignment mark is shifted in the same direction and amount as mentionedabove. As a result, the opening portion of the printed mask iscoincident with the opening portion of the solder resist layer, so thatan opening volume of the printed mask is not decreased due to the solderresist layer and the height of a solder bump is not lowered.

In FIG. 41, the pad 21 for the solder bump formation (conductor pattern)may be covered with the opening peripheral edge of the solder resistlayer or may perfectly be exposed in the opening portion.

As mentioned above, in the above structures {circle around (1)}, {circlearound (2)}, {circle around (4)} of the printed circuit board accordingto the invention, the inner layer side of the conductor is constructedwith the electroless plated film which is harder than the electrolyticplated film, and hence the peel strength is never lowered. Because thehigher the hardness of the portion contacting with an interlaminarinsulating layer and located in the inner layer side of the conductorcircuit (in case of adopting an adhesive for electroless plating asmentioned later as an interlaminar insulating layer, the portioncontacting with a roughened surface), the higher the peel strength. Evenwhen the printed circuit board according to the invention is mountedwith an IC chip and subjected to a heat cycle test under −55° C.-+125°C., the occurrence of cracks generated in the interlaminar insulatingresin layer starting from the conductor circuit or the viahole, andcracks generated in the solder resist layer starting from the boundarybetween the side face of the conductor layer and the solder resist layercontacting therewith can be prevented, and also the peeling of theconductor circuit, the viahole or the solder resist layer is notobserved.

Moreover, the printed circuit board having such a structures {circlearound (1)}˜{circle around (4)} can easily be produced by the productionmethod according to the invention mentioned later (semi-additiveprocess).

In the invention, it is desirable that the roughened layer formed on thesurface of the conductor circuit, the surface of the viahole or thesurface of the conductor layer for an alignment mark is a roughenedsurface of copper formed by an etching treatment, a polishing treatment,an oxidation treatment or a redox treatment, or a roughened surface of aplated film formed by subjecting to a plating treatment.

Particularly, it is desirable that the roughened layer is an alloy layercomposed of copper-nickel-phosphorus. Because the alloy layer is aneedle-shaped crystal layer and is excellent in adhesion to the solderresist layer. Further, the alloy layer is electrically conductive, andhence even if the solder body is formed on the surface of the pad, theremoval of the alloy layer is not necessary.

The composition of the alloy layer is desirably 90-96 wt % of copper,1-5 wt % of nickel and 0.5-2 wt % of phosphorus because theneedle-shaped structure is obtained in such a composition ratio.

Moreover, FIG. 18 is a triangular diagram of three components showing acomposition of copper-nickel-phosphorus capable of forming theneedle-shaped crystal. In this figure, the range surrounded by (Cu, Ni,P)=(100, 0, 0), (90, 10, 0), (90, 0, 10) is preferable.

When the roughened layer is formed by the oxidation treatment, it isdesirable to use a solution of an oxidizing agent comprising sodiumchlorite, sodium hydroxide and sodium phosphate.

When the roughened layer is formed by the redox treatment, it isdesirably carried out by immersing a solution of a reducing agentcomprising sodium hydroxide and sodium borohydride after the aboveoxidation treatment.

The roughened layer formed on the surface of the conductor circuitdesirably has a thickness of 0.5-10 μm, preferably 0.5-7 μm. Because, ifthe thickness is too thick, the roughened layer itself is apt to bedamaged and peeled, while if it is too thin, adhesion is lowered.

In the invention, the electroless plated film constituting the conductorcircuit desirably has a thickness of 0.1-5 μm, preferably 0.5-3 μm.Because, if the thickness is too thick, the ability to follow theinterlaminar insulating resin layer lowers, while if it is too thin,degradation of peel strength is caused and electric resistance becomeslarge in the case of being subjected to an electrolytic plating to causescattering in the thickness of the plated film.

Furthermore, the electrolytic plated film constituting the conductorcircuit desirably has a thickness of 5-30 μm, preferably 10-20 μm.Because, if the thickness is too thick, degradation of peel strength iscaused, while if it is too thin, the ability to follow the interlaminarinsulating resin layer lowers.

Thus, in the invention, the conductor circuit is comprised of theelectrolytic plated film and the electroless plated film, and theroughened layer formed on the surface of the conductor circuit mainlycontacts with the electrolytic plated film. The electrolytic plated filmis apt to be dissolved by local electrode reaction as compared with theelectroless plated film, so that when the electrolytic plated film formsthe local electrode with the roughened layer, it is rapidly dissolvedand hence a large hole is apt to be formed in the surface of theconductor circuit. In the invention, therefore, it is particularlydesirable that the surface of the roughened layer is covered with alayer of a metal having an ionization tendency of more than copper butless than titanium or a noble metal, which is another feature in thispoint. Thus, the dissolution of the conductor circuit through the localelectrode reaction can be controlled.

As the metal having an ionization tendency not lower than that of copperbut not higher than that of titanium, there is at least one metalselected from the group consisting of titanium, aluminum, zinc, iron,indium, thallium, cobalt, nickel, tin, lead and bismuth.

As the noble metal, there is at least one metal selected from the groupconsisting of gold, silver and platinum.

Such a metal or noble metal layer covering the roughened layer canprevent the dissolution of the conductor circuit through the localelectrode reaction caused in the roughening of the interlaminarinsulating layer.

Such a metal or noble metal layer desirably has a thickness of 0.1-2 μm.

Among such a metal or noble metal, tin is preferable. Tin can form athin layer through an electroless substitution plating and canadvantageously follow the roughened layer.

In the invention, it is desirable that the roughened layer is formed onat least a side face of the conductor circuit. Because cracks generatedin the interlaminar insulating resin layer due to the heat cycle resultfrom the bad adhesion between the side face of the conductor circuit andthe insulating resin layer, but in such a structure according to theinvention, the cracks generated in the interlaminar insulating resinlayer starting from the boundary between the side face of the conductorcircuit and the insulating resin layer can be prevented.

In the invention, it is desirable that the adhesive for electrolessplating is used as the interlaminar insulating resin layer constitutingthe above wiring substrate. The adhesive for electroless plating isoptimum to be obtained by dispersing cured heat-resistant resinparticles soluble in acid or oxidizing agent into an uncuredheat-resistant resin hardly soluble in acid or oxidizing agent throughcuring.

Because, the heat-resistant resin particles can be dissolved and removedby treating with an acid or an oxidizing agent to form a roughenedsurface of octopus-trap shaped anchors on its surface.

In the adhesive for electroless plating, the cured heat-resistant resinparticles are desirable to be selected from {circle around (1)}heat-resistant resin powder having an average particle size of not morethan 10 μm, {circle around (2)} aggregated particles formed byaggregating heat-resistant resin powder having an average particle sizeof not more than 2 μm, {circle around (3)} a mixture of heat-resistantresin powder having an average particle size of 2-10 μm andheat-resistant resin powder having an average particle size of not morethan 2 μm, {circle around (4)} false particles formed by adhering atleast one of heat-resistant resin powder and inorganic powder having anaverage particle size of not more than 2 μm onto surfaces ofheat-resistant resin powder having an average particle size of 2-10 μm,and {circle around (5)} a mixture of heat-resistant resin powder havingan average particle size of 0.1-0.8 μm and heat-resistant resin powderhaving an average particle size of more than 0.8 μm but less than 2 μmbecause they can form complicated anchor.

A method of producing the printed circuit board according to theinvention will be described below.

(1) At first, a wiring substrate is prepared by forming an inner layercopper pattern on a surface of a core substrate.

The copper pattern of the wiring substrate is formed by a method ofetching a copper-clad laminate, or a method of forming an adhesive layerfor electroless plating on a substrate such as glass epoxy substrate,polyimide substrate, ceramic substrate, metal substrate or the like androughening the surface of the adhesive layer and subjecting theroughened surface to an electroless plating, or so called semi-additiveprocess (the whole of the roughened surface is subjected to anelectroless plating and then a plating resist is formed thereon and aportion not forming the plating resist is subjected to an electrolyticplating and the plating resist is removed and etched to form a conductorcircuit comprised of an electrolytic plated film and an electrolessplated film).

If necessary, a roughened layer of copper-nickel-phosphorus is furtherformed on the copper pattern surface of the wiring substrate.

The roughened layer is formed by an electroless plating. The compositionof the electroless plating aqueous solution desirably has a copper ionconcentration of 2.2×10⁻²˜4.1×10⁻² mol/l, a nickel ion concentration of2.2×10⁻³˜4.1×10⁻³ mol/l and a hypophosphorus acid ion concentration of0.20˜0.25 mol/l.

The film deposited within the above range has a needle in crystalstructure and is excellent in the anchor effect. The electroless platingaqueous solution may be added with a complexing agent and additives inaddition to the above compounds.

As the other method of forming the roughened layer, there areoxidation-reduction treatment, a method of etching copper surface alonggrain boundary to form a roughened layer and the like.

Moreover, through-holes are formed in the core substrate, and the frontand back wiring layers may be electrically connected to each otherthrough the through-holes.

And also, a resin may be filled in the through-holes and between theconductor circuits of the core substrate to ensure the smoothnessthereof (see FIGS. 1-4).

(2) Then, an interlaminar insulating resin layer is formed on theprinted wiring substrate prepared in step (1).

In the invention, it is particularly desirable to use an adhesive forelectroless plating as the interlaminar insulating resin material (seeFIG. 5).

(3) After the adhesive layer for electroless plating formed in step (2)is dried, an opening portion for the formation of viahole is formed, ifnecessary.

The opening portion for the formation of viahole is formed in theadhesive layer by light exposure, development and thermosetting in thecase of photosensitive resin, or by thermosetting and laser working inthe case of thermosetting resin (see FIG. 6).

(4) Then, epoxy resin particles existing on the surface of the curedadhesive layer are dissolved and removed with an acid or an oxidizingagent to roughen the surface of the adhesive layer (see FIG. 7).

As the acid, there are phosphoric acid, hydrochloric acid, sulfuricacid, and an organic acid such as formic acid, acetic acid or the like.Particularly, the use of the organic acid is desirable because it hardlycorrodes the metal conductor circuit exposed from the viahole by theroughening treatment.

As the oxidizing agent, it is desirable to use chromic acid,permanganate (potassium permanganate or the like) and so on.

(5) Then, a catalyst nucleus is applied to the wiring substrate providedwith the roughened surface of the adhesive layer.

In the application of the catalyst nucleus, it is desirable to use anoble metal ion, a noble metal colloid or the like. In general,palladium chloride or palladium colloid is used. Moreover, it isdesirable to conduct a heating treatment for fixing the catalystnucleus. As the catalyst nucleus, palladium is favorable.

(6) Then, the surface of the adhesive layer for electroless plating issubjected to an electroless plating to form an electroless plated filmon the whole of the roughened surface (see FIG. 8). In this case, thethickness of the electroless plated film is 0.1˜5 μm, more particularly0.5˜3 μm.

Then, a plating resist is formed on the electroless plated film (seeFIG. 9). As the plating resist, it is particularly desirable to use acomposition comprised of an imidazole curing agent and an acrylate ofcresol type epoxy resin, phenol novolac type epoxy resin or the like,but use may be made of commercially available products.

(7) Then, a portion not forming the plating resist is subjected to anelectrolytic plating to form conductor circuits and viaholes (see FIG.10). In this case, it is desirable that the thickness of theelectrolytic plated film is 5˜30 μm.

As the electrolytic plating, it is desirable to use an electrolyticcopper plating.

(8) After the plating resist is removed, the electroless plated filmbeneath the plating resist is removed by dissolving in an etchingsolution such as a mixture of sulfuric acid and hydrogen peroxide,sodium persulfate, ammonium persulfate or the like to obtain anindependent conductor circuit (see FIG. 11).(9) Then, a roughened layer is formed on the surface of the conductorcircuit (see FIG. 12).

As the method of forming the roughened layer, there are etchingtreatment, polishing treatment, redox treatment and plating treatment.

Among them, the redox treatment is conducted by using an oxidationaqueous solution of NaOH (10 g/l), NaClO₂ (40 g/l) and Na₃PO₄ (6 g/l)and a reduction aqueous solution of NaOH (10 g/l) and NaBH₄ (6 g/l).

Furthermore, the roughened layer made from copper-nickel-phosphorusalloy layer is formed by deposition through electroless plating.

As the electroless alloy plating aqueous solution, it is favorable touse a plating bath of aqueous solution composition comprising coppersulfate: 1˜40 g/l, nickel sulfate: 0.1˜6.0 g/l, citric acid: 10˜20 g/l,hypophosphite: 10˜100 g/l, boric acid: 10˜40 g/l and surfactant: 0.01˜10g/l.

In the invention, if necessary, it is desirable to cover the surface ofthe roughened layer with a layer of a metal having an ionizationtendency of more than copper but less than titanium or a noble metal.

In the case of tin, a solution of tin borofluoride-thiourea or tinchloride-thiourea is used. In this case, Sn layer having a thickness ofabout 0.1˜2 μm is formed through Cu—Sn substitution reaction.

In the case of the noble metal, there may be adopted sputtering method,vaporization method and the like.

(10) An adhesive layer for electroless plating as an interlaminarinsulating resin layer is formed on the substrate (see FIG. 13).

(11) Then, an upper layer conductor circuit is formed by repeating steps(3)-(8) (see FIGS. 14-17). In this case, a roughened layer may be formedon the surfaces of the conductor circuits in the same manner as in thestep (9), and it is particularly desirable that the roughened layer isformed on the surface of the conductor layer serving as an alignmentmark and a pad for a solder bump formation. In view of the above, theprinted circuit board may be formed by laminating a first interlaminarinsulating layer on a conductor circuit of a substrate and repeatingformation of conductor circuit and an interlaminar insulating layer onthe first interlaminar insulating layer.(12) Then, a solder resist composition is applied onto both surfaces ofthe thus obtained wiring substrate and the coating film of the solderresist composition is dried. Then, a photomask film depicted with anopening portion is placed on the dried film, which is subjected to lightexposure and developing treatments to form an opening portion exposing aportion of the conductor layer serving as a pad portion for a solderbump formation and an alignment mark in the conductor circuit.

The opening size of the opening portion coresponding to the pad portionfor the solder bump formation may be made larger than the diameter ofthe pad to completely expose the pad or may be made smaller than thediameter of the pad so as to cover the peripheral edge of the pad withthe solder resist. Particularly, when the opening size is smaller thanthe diameter of the pad, the roughened layer on the pad surface isclosely adhered to the solder resist, so that the pad can be restrainedby the solder resist to prevent peeling of the pad. On the other hand,the conductor layer serving as the alignment mark is covered at itsperipheral edge with the solder resist so as not to completely exposethe opening portion of the solder resist layer.

(13) Then, a metal layer of nickel-gold is formed on the pad portionexposed from the opening portion.

(14) Then, a solder body is fed onto the pad exposed from the openingportion.

As a method of feeding the solder body, use may be made of a soldertransferring method and a solder printing method.

The solder transferring method is a method wherein a solder foil isattached to a prepreg and etched so as to leave only a portioncorresponding to the opening portion to render into a solder carrierfilm having a solder pattern, and the solder carrier film is laminatedso as to contact the solder pattern with the pad after a flux is appliedto the opening portion in the solder resist of the substrate and heatedto transfer the solder onto the pad. On the other hand, the solderprinting method is a method wherein a metal mask having through-holescorresponding to the pads is placed on to the substrate and a solderpaste is printed and heated.

The following examples are given in illustration of the invention andare not intended as limitations thereof.

EXAMPLE 1

(1) As a starting material, there is used a copper-clad laminateobtained by laminating a copper foil 8 of 18 μm on each surface of asubstrate 1 made from a glass epoxy resin or BT (bismaleimide triazine)resin having a thickness of 0.6 mm (see FIG. 1). The copper foil 8 ofthe copper-clad laminate is etched in a pattern according to the usualmanner, which is pierced and subjected to an electroless plating to forminnerlayer conductor circuits 4 and through-holes 9 on both surfaces ofthe substrate (see FIG. 2).

Further, bisphenol F epoxy resin is filled between the innerlayerconductor circuits 4 and in the through-holes 9 (see FIG. 3).

(2) The substrate treated in step (1) is washed with water, dried,acidically degreased and soft-etched. Then, the substrate is treatedwith a catalyst solution comprising palladium chloride and organic acidto give a Pd catalyst, which is activated and subjected to a plating inan electroless plating bath comprising 8 g/l of copper sulfate, 0.6 g/lof nickel sulfate, 15 g/l of citric acid, 29 g/l of sodiumhypophosphite, 31 g/l of boric acid and 0.1 g/l of surfactant and havingpH=9 to form a roughened layer 11 (uneven layer) of Cu—Ni—P alloy havinga thickness of 2.5 μm on the surface of the copper conductor circuits 4(see FIG. 4).(3) A photosensitive adhesive solution (interlaminar resin insulatingagent) is prepared by mixing 70 parts by weight of 25% acrylated productof cresol novolac epoxy resin (made by Nippon Kayaku Co., Ltd. molecularweight: 2500) dissolved in DMDG (diethylene glycol dimethyl ether), 30parts by weight of polyether sulphone (PES), 4 parts by weight of animidazole curing agent (made by Shikoku Kasei Co., Ltd. trade name:2E4MZ-CN), 10 parts by weight of caprolacton-modified tris(acroxyethyl)isocyanurate (made by Toa Gosei Co., Ltd. trade name: Aronix M325) as aphotosensitive monomer, 5 parts of benzophenone (made by Kanto KagakuCo., Ltd.) as a photoinitiator, 0.5 parts by weight of Micheler's ketone(made by Kanto Kagaku Co., Ltd.) as a photosensitizer and 35 parts byweight at 5.5 μm on average and 5 parts by weight at 0.5 μm on averageof epoxy resin particles, adding NMP (normal methyl pyrolidone),adjusting a viscosity to 12 Pa·s in a homodisper agitating machine andkneading them through three rolls.(4) The photosensitive adhesive solution obtained in step (3) is appliedonto both surfaces of the substrate treated in step (2) by means of aroll coater and left to stand at a horizontal state for 20 minutes anddried at 60° C. for 30 minutes to form an adhesive layer 2 having athickness of 60 μm (see FIG. 5).(5) A photomask film depicted with viaholes is adhered onto each surfaceof the substrate provided with the adhesive layer 2 in step (4) andexposed by irradiation of ultraviolet ray.(6) The substrate exposed in step (5) is developed by spraying DMTG(triethylene glycol dimethylether) solution to form openings forviaholes of 100 μmφ in the adhesive layer 2. Further, the substrate isexposed to a superhigh pressure mercury lamp at 3000 mJ/cm² and thenheated at 100° C. for 1 hour and at 150° C. for 5 hours to form anadhesive layer 2 of 50 μm in thickness having the openings (opening 6for the formation of viahole) with an excellent size accuracycorresponding to the photomask film (see FIG. 6). Moreover, theroughened layer 11 is partially exposed in the opening 6 for theviahole.(7) The substrate provided with the openings 6 for the viaholes in steps(5), (6) is immersed in chromic acid for 2 minutes to dissolve andremove epoxy resin particles from the surface of the adhesive layer,whereby the surface of the adhesive layer 2 is roughened. Thereafter, itis immersed in a neutral solution (made by Shipley) and washed withwater (see FIG. 7).(8) A palladium catalyst (made by Atotec Co., Ltd.) is applied to thesubstrate subjected to a roughening treatment (roughening depth: 5 μm)in step (7) to give a catalyst nucleus to the surface of the adhesivelayer 2 and the opening 6 for the viahole.(9) The substrate is immersed in an electroless copper plating bathhaving the following composition to form an electroless copper platedfilm 12 having a thickness of 3 μm over the full roughened surface (seeFIG. 8).[Electroless Plating Aqueous Solution]

EDTA 150 g/l Copper sulfate 20 g/l HCHO 30 ml/l NaOH 40 g/l α,α′bipyridyl 80 mg/l PEG 0.1 g/l[Electroless Plating Condition]

liquid temperature of 70° C., 30 minutes

(10) A commercially available photosensitive dry film is attached to theelectroless copper plated film 12 formed in step (9) and a photomaskfilm is placed on the dry film, which is exposed to a light at 100mJ/cm² and developed with a solution of 0.8% sodium carbonate to form aplating resist 3 having a thickness of 15 μm (see FIG. 9).(11) Then, the non-resist forming portion is subjected to anelectrolytic copper plating under the following conditions to form anelectrolytic copper plated film 13 having a thickness of 15 μm (see FIG.10).[Electrolytic Plating Aqueous Solution]

sulfuric aid 180 g/l copper sulfate 80 g/l additive (made by AtotechJapan 1 ml/l Co., Ltd. trade name: Capalacido GL)[Electrolytic Plating Condition]

current density 1 A/dm² time 30 minutes temperature room temperature(12) After the plating resist 3 is peeled and removed with 5% KOH, theelectroless plated film 12 beneath the plating resist 3 is dissolved andremoved by etching with a mixed solution of sulfuric acid and hydrogenperoxide to form conductor circuits 5 (including viaholes 7) of 18 μm inthickness comprised of the electroless copper plated film 12 and theelectrolytic copper plated film 13 (see FIG. 11).(13) The substrate provided with the conductor circuits 5 is immersed inan electroless plating aqueous solution comprising 8 g/l of coppersulfate, 0.6 g/l of nickel sulfate, 15 g/l of citric acid, 29 g/l ofsodium hypophosphite, 31 g/l of boric acid and 0.1 g/l of surfactant andhaving pH=9 to form a roughened layer 11 of copper-nickel-phosphorushaving a thickness of 3 μm on the surface of the conductor circuit 5(see FIG. 12). When the roughened layer 11 is analyzed by EPMA (electroprobe microanalysis), it shows a composition ratio of Cu: 98 mol %, Ni:1.5 mol % and P: 0.5 mol %.(14) Steps (4)-(12) are repeated to further form an upper layerconductor circuits (including viaholes and alignment marks) to therebyproduce a wiring substrate (see FIGS. 13-17).(15) On the other hand, a solder resist composition is prepared bymixing 46.67 g of a photosensitized oligomer (molecular weight: 4000) inwhich 50% of epoxy group in 60% by weight of cresol novolac epoxy resin(made by Nippon Kayaku Co., Ltd.) dissolved in DMDG is acrylated, 15.0 gof 80% by weight of bisphenol A epoxy resin (made by Yuka Shell Co.,Ltd. trade name: Epikote 1001) dissolved in methyl ethyl ketone, 1:6 gof an imidazole curing agent (made by Shikoku Kasei Co., Ltd. tradename: 2E4MZ-CN), 3 g of a polyvalent acrylic monomer (made by NipponKayaku Co., Ltd. trade name: R604) as a photosensitive monomer, 1.5 g ofa polyvalent acrylic monomer (made by Kyoeisha Kagaku Co., Ltd. tradename: DPE6A), 0.71 g of a dispersion type deforming agent (made bySannopuko Co., Ltd. trade name: S-65), 2 g of benzophenone (made byKanto Kagaku Co., Ltd.) as a photoinitiator and 0.2 g of Micheler'sketone (made by Kanto Kagaku Co., Ltd.) as a photosensitizer andadjusting a viscosity to 2.0 Pa·s at 25° C.

Moreover, the measurement of the viscosity is carried out by means of aB-type viscometer (made by Tokyo Keiki Co., Ltd. DVL-B model) with arotor No. 4 in case of 60 rpm or a rotor No. 3 in case of 6 rpm.

(16) The above solder resist composition is applied onto the wiringsubstrate obtained in step (14) at a thickness of 20 μm. Then, thesubstrate is dried at 70° C. for 20 minutes and at 70° C. for 30 minutesand a photomask film is placed thereon and then exposed to ultravioletrays at 1000 mJ/cm² and developed with DMTG. Further, it is heated at80° C. for 1 hour, at 100° C. for 1 hour, at 120° C. for 1 hour and at150° C. for 3 hours to form a solder resist layer 14 (thickness: 20 μm)opened in the pad portion (opening size: 200 μm).(17) The substrate provided with the solder resist layer 14 is immersedin an electroless nickel plating solution of pH=5 comprising 30 g/l ofnickel chloride, 10 g/l of sodium hypophosphite and 10 g/l of sodiumcitrate for 20 minutes to form a nickel plated layer 15 having athickness of 5 μm in the opening portion. Further, the substrate isimmersed in an electroless gold plating solution comprising 2 g/l ofpotassium gold cyanide, 75 g/l of ammonium chloride, 50 g/l of sodiumcitrate and 10 g/l of sodium hypophosphite at 93° C. for 23 seconds toform a gold plated layer 16 having a thickness of 0.03 μm on the nickelplated layer 15.(18) A solder paste is printed on the opening portion of the solderresist layer 14 and reflowed at 200° C. to form solder bumps 17, wherebythere is produced a printed circuit board having solder bumps 17.

EXAMPLE 2

A multilayer printed circuit board having solder bumps is produced inthe same manner as in Example 1 except that the roughening of theconductor circuit is carried out by etching. In this case, an etchingsolution of Durabond (trade name, made by Meck Co., Ltd.) is used.

EXAMPLE 3

A multilayer printed circuit board having solder bumps is produced inthe same manner as in Example 1 except that after the roughening of theconductor circuit is carried out, Cu—Sn substitution reaction is carriedout by immersing in a solution of 0.1 mol/l of tin borofluoride and 1.0mol/l of thiourea at a temperature of 50° C. and pH=1.2 to form a Snlayer having a thickness of 0.3 μm on the surface of the roughened layer(the Sn layer is not shown).

EXAMPLE 4

A multilayer printed circuit board having solder bumps is produced inthe same manner as in Example 1 except that the roughening of theconductor circuit is carried out by etching. In this case, an etchingsolution of Durabond (trade name, made by Meck Co., Ltd.) is used.Further, an Au layer having a thickness of 0.5 μm is formed on thesurface of the roughened layer by sputtering.

EXAMPLE 5

A. Preparation of an Adhesive Composition for Electroless Plating

{circle around (1)}. 35 parts by weight of a resin solution obtained bydissolving 25% acrylated product of cresol novolac epoxy resin (made byNippon Kayaku Co., Ltd. molecular weight: 2500) in DMDG at aconcentration of 80 wt % is mixed with 3.15 parts by weight of aphotosensitive monomer (made by Toa Gosei Co., Ltd. trade name: AronixM315), 0.5 parts by weight of a defoaming agent (made by Sannopuko Co.,Ltd. trade name: S-65) and 3.6 parts by weight of NMP with stirring.{circle around (2)}. 12 parts by weight of polyether sulphone (PES) ismixed with 7.2 parts by weight at 1.0 μm on average and 3.09 parts byweight at 0.5 μm on average of epoxy resin particles (made by SanyoKasei Co., Ltd. trade name: Polymerpole) and further added with 30 partsby weight of NMP and mixed in a beads mill with stirring.{circle around (3)}. 2 parts by weight of an imidazole curing agent(made by Shikoku Kasei Co., Ltd. trade name: 2E-4MZ-CN) is mixed with 2parts by weight of a photoinitiator (made by Ciba Geigey, trade name:Irgaquar I-907), 0.2 parts by weight of a photosensitizer (made byNippon Kayaku Co., Ltd. trade name: DETX-S) and 1.5 parts by weight ofNMP with stirring.

These mixtures are mixed to prepare an adhesive composition forelectroless plating.

B. Preparation of an Underlayer Interlaminar Insulating Resin Material

{circle around (1)}. 35 parts by weight of a resin solution obtained bydissolving 25% acrylated product of creasol novolac epoxy resin (made byNippon Kayaku Co., Ltd. molecular weight: 2500) in DMDG at aconcentration of 80 wt % is mixed with 4 parts by weight of aphotosensitive monomer (made by Toa Gosei Co., Ltd. trade name: AronixM315), 0.5 parts by weight of a defoaming agent (made by Sannopuko Co.,Ltd. trade name: S-65) and 3.6 parts by weight of NMP with stirring.{circle around (2)}. 12 parts by weight of polyether sulphone (PES) ismixed with 14.49 parts by weight at 0.5 μm on average of epoxy resinparticles (made by Sanyo Kasei Co., Ltd. trade name: Polymerpole) andfurther added with 30 parts by weight of NMP and mixed in a beads millwith stirring.{circle around (3)}. 2 parts by weight of an imidazole curing agent(made by Shikoku Kasei Co., Ltd. trade name: 2E-4MZ-CN) is mixed with 2parts by weight of a photoinitiator (made by Ciba Geigey, trade name:Irgaquar I-907), 0.2 parts by weight of a photosensitizer (made byNippon Kayaku Co., Ltd. trade name: DETX-S) and 1.5 parts by weight ofNMP with stirring.

These mixtures are mixed to prepare a resin composition used as anunderlayer side insulating layer constituting the interlaminarinsulating resin layer of two-layer structure.

C. Preparation of a Resin Filler

{circle around (1)}. 100 parts by weight of bisphenol F epoxy monomer(made by Yuka Shell Co., Ltd. trade name: YL983U, molecular weight:310), 170 parts by weight of SiO₂ spherical particles having an averageparticle size of 1.6 μm and coated on its surface with a silane couplingagent (made by Adomatic Co., Ltd. trade name: CRS 1101-CE, the maximumsize of the particles is not more than the thickness (15 μm) ofinnerlayer copper pattern as mentioned below) and 1.5 parts by weight ofa leveling agent (made by Sannopuko Co., Ltd. trade name: Perenol S4)are kneaded through three rolls and a viscosity thereof is adjusted to45,000-49,000 cps at 23±1° C.{circle around (2)}. 6.5 parts by weight of an imidazole curing agent(made by Shikoku Kasei Co., Ltd. trade name: 2E4MZ-CN)

They are mixed to prepare a resin filler 10.

D. Production of Printed Circuit Board

(1) As a starting material, there is used a copper-clad laminate formedby laminating a copper foil 8 of 18 μm in thickness onto each surface ofa substrate 1 made from glass epoxy resin or BT (bismaleimide triazine)resin and having a thickness of 1 mm (see FIG. 21). At first, thecopper-clad laminate is drilled and a plating resist is formed thereon,which is subjected to an electroless plating treatment to formthrough-holes 9 and further the copper foil 8 is etched in a patternaccording to the usual manner to form innerlayer copper patterns 4 onboth surfaces of the substrate 1.(2) The substrate provided with the innerlayer copper pattern 4 andthrough-hole 9 is washed with water, dried and subjected to a redoxtreatment using an oxidizing aqueous solution of NaOH (10 g/l), NaClO₂(40 g/l) and Na₃PO₄ (6 g/l) and a reducing aqueous solution of NaOH (10g/l) and NaBH₄ (6 g/l) to form a roughened layer 11 on the surfaces ofthe innerlayer copper pattern 4 and the through-hole 9 (see FIG. 22).(3) The resin filler 10 is applied onto both surfaces of the substrateby means of a roll coater to fill between the conductor circuits 4 andin the through-holes 9 and dried at 70° C. for 20 minutes. Similarly,the resin filler 10 is filled between the conductor circuits 4 and inthe through-hole 9 on the other-side surface and then dried by heatingat 70° C. for 20 minutes (see FIG. 23).(4) The one-side surface of the substrate treated in step (3) ispolished by a belt sander polishing using #600 belt polishing paper(made by Sankyo Rikagaku Co., Ltd.) in such a manner that the resinfiller is not left on the surface of the innerlayer copper pattern 4 orthe land surface of the through-hole 9, and then buff-polished so as toremove scratches formed by the belt sander polishing. Such a series ofpolishings is applied to the other surface of the substrate.

Then, the substrate is heated at 100° C. for 1 hour, at 120° C. for 3hours, at 150° C. for 1 hour and at 180° C. for 7 hours to cure theresin filler 10 (see FIG. 24).

Thus, the roughened layers 11 formed on the surface layer portion of theresin filler 10 filled in the through-hole 9 and the like and on theupper surface of the innerlayer conductor circuits 4 are removed tosmoothen both surfaces of the substrate, whereby there is obtained awiring substrate wherein the resin filler 10 is strongly adhered to theside surface of the innerlayer conductor circuit 4 through the roughenedlayer 11 and the inner wall surface of the through-hole 9 is stronglyadhered to the resin filler 10 through the roughened layer 11. That is,the surface of the resin filler 10 and the surface of the innerlayercopper pattern 4 are the same plane in this step. In this case, thecuring resin filled has a Tg point of 155.6° C. and a linear thermalexpansion coefficient of 44.5×10⁻⁶/° C.

(5) A roughened layer (uneven layer) 11 of Cu—Ni—P alloy having athickness of 2.5 μm is formed on the exposed surfaces of the innerlayerconductor circuit 4 and the land of the through-hole 9 of step (4) andfurther a Sn layer having a thickness of 0.3 μm is formed on the surfaceof the roughened layer 11 (see FIG. 25, provided that the Sn layer isnot shown).

The formation method is as follows. That is, the substrate is acidicallydegreased and soft-etched and treated with a catalyst solution ofpalladium chloride and organic acid to give Pd catalyst, which isactivated and subjected to a plating in an electroless plating bath ofpH=9 comprising 8 g/l of copper sulfate, 0.6 g/l of nickel sulfate, 15g/l of citric acid, 29 g/l of sodium hypophosphite, 31 g/l of boricacid, 0.1 g/l of surfactant and water to form the roughened layer 11 ofCu—Ni—P alloy on the upper surfaces of the copper conductor circuit 4and land of through-hole 9. Then, Cu—Sn substitution reaction is carriedout by immersing in a solution containing 0.1 mol/l of tin borofluorideand 1.0 mol/l of thiourea at a temperature of 50° C. and pH=1.2 to formthe Sn layer of 0.3 μm on the surface of the roughened layer 11 (Snlayer is not shown).

(6) The interlaminar insulating resin material of the item B (viscosity:1.5 Pa·s) is applied onto both surfaces of the substrate treated in step(5) by means of a roll coater and left to stand at a horizontal statefor 20 minutes and dried at 60° C. for 30 minutes (pre-baking) to forman insulating layer 2 a.

Further, the adhesive for electroless plating of item A (viscosity: 7Pa·s) is applied onto the insulating layer 2 a by means of a roll coaterand left to stand at a horizontal state for 20 minutes and dried at 60°C. for 30 minutes (pre-baking) to form an adhesive layer 2 b (see FIG.26).

(7) A photomask film depicted with black circles of 85 μm in diameter isclosely adhered onto both surfaces of the substrate provided with theinsulating layer 2 a and the adhesive layer 2 b in step (6) and exposedto a superhigh pressure mercury lamp at 500 mJ/cm². It is developed byspraying DMTG solution and further exposed to a superhigh pressuremercury lamp at 3000 mJ/cm² and heated at 100° C. for 1 hour and at 150°C. for 5 hours (post baking) to form an interlaminar insulating resinlayer (two-layer structure) of 35 μm in thickness having openings of 85μm in diameter (openings 6 for the formation of viaholes) with anexcellent size accuracy corresponding to the photomask film (see FIG.27). Moreover, the tin plated layer is partially exposed in the openingfor viahole.(8) The substrate provided with the openings is immersed in 800 g/l ofchromic acid at 70° C. for 19 minutes to dissolve and remove the epoxyresin particles existing on the surface of the adhesive layer 2 b in theinterlaminar insulating resin layer 2, whereby the surface of theinterlaminar insulating resin layer 2 is roughened (depth: 3 μm) andthereafter the substrate is immersed in a neutral solution (made byShipley) and washed with water (see FIG. 28).

Further, a palladium catalyst (made by Atotec Co., Ltd.) is applied tothe roughened surface of the substrate to give a catalyst nucleus to thesurface of the interlaminar insulating resin layer 2 and the inner wallsurface of the opening 6 for viahole.

(9) The substrate is immersed in an electroless copper plating bathhaving the following composition to form an electroless copper platedfilm 12 having a thickness of 0.6 μm on the full roughened surface (seeFIG. 29).

[Electroless Plating Aqueous Solution]

EDTA 150 g/l Copper sulfate 20 g/l HCHO 30 ml/l NaOH 40 g/lα,α′-bipyridyl 80 mg/l PEG 0.1 g/l[Electroless Plating Condition]

liquid temperature of 70° C., 30 minutes

(10) A commercially available photosensitive dry film is adhered to theelectroless copper plated film 12 formed in step (9) and a mask isplaced thereon and exposed to a light at 100 mJ/cm² and developed with0.8% of sodium carbonate to form a plating resist 3 having a thicknessof 15 μm (see FIG. 30).(11) Then, the non-resist forming portion is subjected to anelectrolytic copper plating under the following conditions to form anelectrolytic copper plated film 13 having a thickness of 15 μm (see FIG.31).[Electrolytic Plating Aqueous Solution]

Sulfuric acid 180 g/l Copper sulfate 80 g/l Additive (made by AtotecJapan. Co., Ltd. 1 ml/l trade name: Capalacid GL)[Electrolytic Plating Condition]

current density 1 A/dm² time 30 minutes temperature Room temperature(12) After the plating resist 3 is peeled off with 5% KOH, theelectroless plated film 12 beneath the plating resist 3 is dissolved andremoved by etching with a mixed solution of sulfuric acid and hydrogenperoxide to form conductor circuit 5 (including viahole) of 18 μm inthickness comprised of the electroless copper plated film 12 and theelectrolytic copper plated film 13. Further, it is immersed in 800 g/lof chromic acid at 70° C. for 3 minutes to etch the surface of theadhesive layer for electroless plating between conductor circuitslocated at the portion not forming the conductor circuit by 1˜2 μm tothereby remove the palladium catalyst remaining on the surface (see FIG.32).(13) The substrate provided with the conductor circuits 5 is immersed inan electroless plating aqueous solution of pH=9 comprising 8 g/l ofcopper sulfate, 0.6 g/l of nickel sulfate, 15 g/l of citric acid, 29 g/lof sodium hypophosphite, 31 g/l of boric acid and 0.1 g/l of surfactantto form a roughened layer 11 of copper-nickel-phosphorus having athickness of 3 μm on the surface of the conductor circuit 5 (see FIG.33). In this case, the resulting roughened layer 11 has a compositionratio of Cu: 98 mol %, Ni: 1.5 mol % and P: 0.5 mol % as analyzed byEPMA (electro probe microanalysis).

Further, Cu—Sn substitution reaction is carried out by immersing in asolution of 0.1 mol/l of tin borofluoride and 1.0 mol/l of thiourea at atemperature of 50° C. and pH=1.2 to form a Sn layer having a thicknessof 0.3 μm on the surface of the roughened layer 11 (the Sn layer is notshown).

(14) Steps (6)-(13) are repeated to further form upper layer conductorcircuits (including viaholes and alignment marks) to thereby produce amultilayer wiring substrate. However, Sn substitution is not conducted(see FIGS. 34-39).

(15) On the other hand, a solder resist composition is prepared bymixing 46.67 g of a photosensitized oligomer (molecular weight: 4000) inwhich 5.0% of epoxy group in 60% by weight of cresol novolac epoxy resin(made by Nippon Kayaku Co., Ltd.) dissolved in DMDG is acrylated, 15.0 gof 80% by weight of bisphenol A epoxy resin (made by Yuka Shell Co.,Ltd. trade name: Epikote 1001) dissolved in methyl ethyl ketone, 1.6 gof an imidazole curing agent (made by Shikoku Kasei Co., Ltd. tradename: 2E4MZ-CN), 3 g of a polyvalent acrylic monomer (made by NipponKayaku Co., Ltd. trade name: R604) as a photosensitive monomer, 1.5 g ofa polyvalent acrylic monomer (made by Kyoeisha Kagaku Co., Ltd. tradename: DPE6A), 0.71 g of a dispersion type deforming agent (made bySannopuko Co., Ltd. trade name: S-65), 2 g of benzophenone (made byKanto Kagaku Co., Ltd.) as a photoinitiator and 0.2 g of Micheler'sketone (made by Kanto Kagaku Co., Ltd.) as a photosensitizer andadjusting a viscosity to 2.0 Pa·s at 25° C.

Moreover, the measurement of the viscosity is carried out by means of aB-type viscometer (made by Tokyo Keiki Co., Ltd. DVL-B model) with arotor No. 4 in case of 60 rpm or a rotor No. 3 in case of 6. rpm.

(16) The above solder resist composition is applied onto both surfacesof the multilayer wiring substrate obtained in step (14) at a thicknessof 20 μm. Then, the substrate is dried at 70° C. for 20 minutes and at70° C. for 30 minutes and a photomask film of 5 mm in thickness depictedwith circle pattern (mask pattern) is placed thereon and then exposed toultraviolet rays at 1000 mJ/cm² and developed with DMTG. Further, it isheated at 80° C. for 1 hour, at 100° C. for 1 hour, at 120° C. for 1hour and at 150° C. for 3 hours to form a solder resist layer 14(thickness: 20 μm) opened in the pad portion (including viahole and itsland portion, opening size: 200 μm).(17) The substrate provided with the solder resist layer 14 is immersedin an electroless nickel plating aqueous solution of pH=5 comprising 30g/l of nickel chloride, 10 g/l of sodium hypophosphite and 10 g/l ofsodium citrate for 20 minutes to form a nickel plated layer 15 having athickness of 5 μm in the opening portion. Further, the substrate isimmersed in an electroless gold plating aqueous solution comprising 2g/l of potassium gold cyanide, 75 g/l of ammonium chloride, 50 g/l ofsodium citrate and 10 g/l of sodium hypophosphite at 93° C. for 23seconds to form a gold plated layer 16 having a thickness of 0.03 μm onthe nickel plated layer 15.(18) A solder paste is printed on the opening portion of the solderresist layer 14 and reflowed at 200° C. to form solder bumps 17 (solderbody), whereby there is produced a printed circuit board having solderbumps (see FIG. 40).

EXAMPLE 6

A printed circuit board having solder bumps is produced in the samemanner as in Example 5 except that a metal film is formed at thefollowing conditions instead of tin substitution.

(6-1) Ti is adhered on the substrate at an atmospheric pressure of 0.6Pa, a temperature of 100° C., an electric power of 200 W and a time of 2minutes. Then, Ti film existing between conductor circuits is etched bychromic acid with resin.

(6-2) Al is adhered on the substrate at an atmospheric pressure of 0.5Pa, a temperature of 100° C., an electric power of 200 W and a time of 1minute. Then, Al film existing between conductor circuits is etched bychromic acid with resin.

(6-3) Zn is adhered on the substrate at an atmospheric pressure of 0.6Pa, a temperature of 100° C., an electric power of 200 W and a time of 2minutes. Then, Zn film existing between conductor circuits is etched bychromic acid with resin.

(6-4) Fe is adhered on the substrate at an atmospheric pressure of 0.6Pa, a temperature of 100° C., an electric power of 200 W and a time of 2minutes. Then, Fe film existing between conductor circuits is etched bychromic acid with resin.

(6-5) In is adhered on the substrate at an atmospheric pressure of 0.6Pa, a temperature of 100° C., an electric power of 200 W and a time of 2minutes. Then, In film existing between conductor circuits is etched bychromic acid with resin.

(6-6) Co is adhered on the substrate at an atmospheric pressure of 0.6Pa, a temperature of 100° C., an electric power of 200 W and a time of 2minutes. Then, Co film existing between conductor circuits is etched bychromic acid with resin.

(6-7) Ni is adhered on the substrate at an atmospheric pressure of 0.6Pa, a temperature of 100° C., an electric power of 200 W and a time of 2minutes. Then, Ni film existing between conductor circuits is etched bychromic acid with resin.

(6-8) The substrate is immersed in an aqueous solution of lead oxide(3.75 g/l), sodium cyanide (26.3 g/l) and sodium hydroxide (105 g/l) asan electroless plating aqueous solution to deposit on the surface of theroughened layer.

(6-9) Bi is adhered on the substrate at an atmospheric pressure of 0.6Pa, a temperature of 100° C., an electric power of 200 W and a time of 2minutes. Then, Bi film existing between conductor circuits is etched bychromic acid with resin.

(6-10) Tl is adhered on the substrate at an atmospheric pressure of 0.6Pa, a temperature of 100° C., an electric power of 200 W and a time of 2minutes. Then, Tl film existing between conductor circuits is etched bychromic acid with resin.

COMPARATIVE EXAMPLE 1

A dry film photo-resist is laminated on the substrate treated in steps(1)-(8) of Example 1, and exposed and developed to form a platingresist. Then, after step (9) of Example 1 is carried out, the platingresist is peeled and removed in the same manner as in step (12) and thewhole surface of the conductor circuit is roughened by step (13) ofExample 1. Thereafter, the formation of interlaminar insulating resinlayer, roughening treatment, the formation of plating resist andelectroless copper plating are carried out in the same manner as inExample 1, and after the plating resist is peeled and removed, amultilayer printed circuit board having solder bumps is produced bycarrying out steps (15)-(19) of Example 1.

COMPARATIVE EXAMPLE 2

A multilayer printed circuit board having solder bumps is produced inthe same manner as in Example 1 except that after the roughening of theconductor circuit, Cu—Sn substitution reaction is carried out byimmersing in a solution of 0.1 mol/l of tin borofluoride and 1.0 mol/lof thiourea at a temperature of 50° C. and pH=1.2 to form a Sn layerhaving a thickness of 0.3 μm on the surface of the roughened layer (theSn layer is not shown).

After IC chip is mounted onto each of the printed circuit boards of theExamples and Comparative Examples, heat cycle tests of 1000 cycles and2000 cycles under conditions of −55° C. for 15 minutes, room temperaturefor 10 minutes and 125° C. for 15 minutes are carried out.

The evaluation of these tests are carried out by confirming occurrencesof cracks in the multilayer printed circuit board by means of a scanningelectron microscope after the test. Further, the presence or absence ofthe peeling at the boundary between viahole and a lower conductorcircuit layer is confirmed in the same manner. Furthermore, the peelstrength is measured according to JIS-C-6481.

The results are shown in Table 1. As seen from the results of thistable, the occurrence of cracks is not observed at about 1000 cycles inthe Examples and Comparative Examples, while the occurrence of cracks isobserved at 2000 cycles in the Comparative Examples. Further, the peelstrength is equal or higher than that of the conductor circuit comprisedof only an electroless plated film.

Thus, in the invention, cracks of the interlaminar insulating resinlayer and peeling at the boundary between viahole and a lower conductorcircuit caused in the heat cycle can be prevented while maintaining apractical peel strength.

Further, the presence or absence of dissolution of the conductor circuitdue to the local electrode reaction is observed by means of an opticalmicroscope. The results are shown in Table 1 with the results of theheat cycle test. As seen from the results of Table 1, in Exampleswherein the surface of the roughened layer is covered with a layer of ametal having an ionization tendency of more than copper but less thantitanium or a noble metal, dissolution of the conductor circuit due tothe local electrode reaction can be controlled.

TABLE 1 Heat cycle test Dissolution Crack of interlaminar of insulatingresin layer Peeling of vianole Peel conductor 1000 cycles 2000 cycles1000 cycles 2000 cycles strength circuit Example 1 none none none none1.2 kg/cm presence 2 none none none none 1.2 kg/cm presence 3 none nonenone none 1.2 kg/cm none 4 none none none none 1.0 kg/cm none 5 nonenone none none 1.0 kg/cm none 6-1 none none none none 1.0 kg/cm none 6-2none none none none 1.0 kg/cm none 6-3 none none none none 1.0 kg/cmnone 6-4 none none none none 1.0 kg/cm none 6-5 none none none none 1.0kg/cm none 6-6 none none none none 1.0 kg/cm none 6-7 none none nonenone 1.0 kg/cm none 6-8 none none none none 1.0 kg/cm none 6-9 none nonenone none 1.0 kg/cm none  6-10 none none none none 1.0 kg/cm noneComparative none presence none presence 0.9 kg/cm presence Example 1Comparative none presence none presence 0.9 kg/cm none Example 2

INDUSTRIAL APPLICABILITY

As mentioned above, according to the invention, it is possible toprevent the occurrence of cracks and the conductor peeling in theinterlaminar insulating layer and dissolution of the conductor circuitdue to the local electrode reaction, so that it is possible to surelyimprove connection reliability of the printed circuit board.

1. A method of producing a multilayer printed circuit board comprising:providing a structure having a substrate, at least one lower conductorcircuit formed over the substrate and having a surface at leastpartially roughened, and an outermost insulating layer formed over thesubstrate and the at least one lower conductor circuit; forming at leastone opening for a viahole structure extending from the outermostinsulating layer to the at least one lower conductor circuit; subjectingthe outermost insulating layer to an electroless plating so as to forman electroless plated film; forming a plating resist on the electrolessplated film; subjecting the plating resist and the electroless platedfilm over the outermost insulating layer to an electrolytic plating soas to form an electrolytic plated film; removing the plating resist;etching and removing the electroless plated film exposed by a pattern ofthe plating resist to form at least one outermost conductor circuitcomprising the electroless plated film and the electrolytic plated film,the viahole structure electrically connecting the lower conductorcircuit and the outermost conductor circuit, and a pad comprising aportion of the viahole structure; roughening a surface of the pad;forming a solder resist layer having at least one opening portion on thepad and covering a peripheral edge of the pad; providing a solder on aportion of the pad exposed from the opening portion of the solder resistlayer; and reflowing the substrate to form solder bumps.
 2. The methodof producing a multilayer printed circuit board according to claim 1,further comprising: forming at least one insulating layer and at leastone conductor circuit between the lower conductor circuit and theoutermost insulating layer.
 3. The method of producing a multilayerprinted circuit board according to claim 1, wherein the opening for theviahole structure is formed by applying a laser beam.
 4. The method ofproducing a multilayer printed circuit board according to claim 1,wherein the surface of the at least one lower conductor circuit is atleast partially roughened by one of etching treatment, polishingtreatment, redox treatment, and plating treatment.
 5. The method ofproducing a multilayer printed circuit board according to claim 1,wherein the outermost insulating layer is subjected to the electrolessplating so as to form the electroless plated film having a thickness of0.1-5 μm, and the plating resist and the electroless plated film overthe outermost insulating layer is subjected to the electrolytic platingso as to form the electrolytic plated film having a thickness of 5-30μm.
 6. The method of producing a multilayer printed circuit boardaccording to claim 1, wherein the providing the solder on the portion ofthe pad is carried out by a screen printing method.